In optical communication systems it is often required to switch optical signals from one optical fibre to another. A variety of optical switching circuits are known for performing this function. For example, U.S. Pat. No. 5,037,169 entitled High Speed Low Loss Optical Switch For Optical Communication Systems in the name of Chun, issued Aug. 6, 1991 discloses a Fabry-Perot etalon utilized as an optical switch for controllably switching an input optical signal on an input optical conduit between first and second output optical conduits.
Another optical switch for switching an input signal from one optical fibre to one of two other optical fibres is described by M. Shirasaki et al. in an article in Applied Optics entitled "Bistable Magnetooptic Switch for Multimode Optical Fiber", published Jun. 1, 1982 Vol. 21, No. 11. Shirasaki describes using a new type of Faraday rotator which utilizes the magnetooptic effect of a yttrium-iron-garnet (YIG) single crystal. The direction of rotation is controlled by inverting the direction in which the magnetic field is applied to the rotator. The optical path is determined by a polarization separator which functions as an optical switch.
As of late, many cable television companies are considering providing services to subscribers via one or more optical fibres instead of a co-axial cable currently used. Furthermore, these companies are considering adapting known optical switching circuits to allow them to monitor whether or not paying subscribers are using particular cable services provided to their homes via optical signals. Although known prior art circuits such as those mentioned above appear to perform their intended functions, there remains a need for a relatively efficient, simple transmissive/reflective switch that will perform the function of allowing a cable company to know when a subscriber is making use of provided services transmitted on an optical fibre. Such a switch would allow companies to monitor an optical fibre and charge their subscribers on a per use basis.
Furthermore, such a switch capable of being switched from a transmissive to a reflective mode, could be used in numerous other applications such as in the aeronautics industry and many others, as will be described later.
It is an object of the invention to provide a relatively inexpensive simple switch which will operate in either a transmitting mode or a reflecting mode.